Extended protection in the rear: The seat belt gets into top shape

Mercedes-Benz is further reinforcing the safety system for passengers in the rear with the active seat-belt buckle and the beltbag. In contrast to many other manufacturers, the seat belts in the rear already include belt tensioners and belt force limiters today.

Both systems were furthermore developed with a particular view toward new markets. There, the occupancy rate in the rear is as much as 30 percent, making it much higher than in Europe. The two systems will be premiered in the next S-Class.

Reducing belt slack: the active seat-belt buckle

With the active seat-belt buckle, an electric motor extends and retracts the belt buckle automatically. In this way, any belt slack in the area of the pelvis and thorax can be reduced so that passengers are secured more firmly in both the sideways and the lengthways direction. The active seat-belt buckle fits in with Mercedes-Benz’s integral safety concept. In keeping with an all-embracing approach to safety, this concept covers all phases of automotive safety: from safety while driving through safety in hazardous situations and protection in the event of an accident to minimisation of the consequences of accidents.

The innovation is classic Mercedes-Benz, improving safety and comfort in one. This is because fastening seat belts in the rear is also made much simpler: the seat belt buckle emerges from the upholstery when the rear doors are opened and is provided with an illuminated insertion slot. Simplifying use of the seat belt in this manner may increase the percentage of rear passengers who buckle up. It also makes it easier to assist children or people who require help in fastening their seat belts.

The active seat-belt buckle is furthermore integrated in the PRE-SAFE® anticipatory safety system. This means that whenever PRE-SAFE® becomes active in critical driving situations or when the system detects the vehicle approaching other objects at a critical speed, reversible belt tensioning is also performed in the rear via the active seat-belt buckle function. The restraint system and the passengers are thus better prepared for a possible accident situation. In this way, the active seat-belt buckle complements the pyrotechnic belt tensioning which has featured as standard on all outer rear seats in Mercedes-Benz vehicles for many years now, and is triggered in the event of an impact exceeding a certain severity.

The active seat-belt buckle is a motorised belt buckle which can be extended upwards by 70 millimetres and retracted by 40 millimetres. The belt buckle is attached via a cable to a nut which runs on a spindle, translating the electric motor’s rotary movement into a linear movement.

The following functions are carried out by means of this movement:

Seat belt reminder/fastening aid: the active seat-belt buckle is provided with an illuminated insertion slot, attracting the occupants’ attention to the buckle. Particularly in the dark, this makes it easier to find the belt buckle and connect it with the seat belt tongue. In addition, the belt buckle is extended by 70 millimetres when occupants enter the rear of the vehicle, to facilitate fastening of the seat belt. When extended, the belt buckle is more readily accessible and it is easier to insert the belt tongue. Both functions are activated when the doors are opened by passengers entering the rear of the vehicle.

Minimised belt slack: after the belt tongue has been inserted, the belt buckle returns to its original position. This reduces any belt slack in the area of the pelvis and thorax, and ensures that the belt fits correctly in the pelvis area.

PRE-SAFE® function for rear occupants: the active seat-belt buckle is fully integrated in the vehicle’s PRE-SAFE® system. Whenever PRE-SAFE® becomes active in critical driving situations or when the system detects the vehicle approaching other objects at a critical speed, reversible belt tensioning is also performed in the rear via the active seat-belt buckle function. The restraint system and the passengers are thus better prepared for a possible accident system. In contrast to its extended position to facilitate fastening of the seat belt, the belt buckle is retracted by approx. 40 millimetres instead. This reversible function increases the belt tensioning on the occupant by up to 80 millimetres. In addition, the belt buckle branches off at a lower point at the occupant’s hip. This reduces the risk of the pelvis submarining under the belt. Securing the occupants more effectively in this way can reduce the strain to which they are exposed in the event of an accident. The active seat-belt buckle complements the pyrotechnic belt tensioning which has featured as standard in Mercedes-Benz vehicles for many years now, and is triggered in the event of an actual impact.

POST-SAFE functionality: to facilitate the rescue of occupants and to assist rescue personnel or the occupants themselves in unbuckling the seat belts, the belt buckle is extended once again as soon as the doors are opened by rescue personnel or the occupants themselves after the system has detected a crash and the vehicle has come to a standstill, provided that the on-board electrical system is intact. The raised belt buckle position allows better access from inside the vehicle, while illumination of the buckle draws attention to the belt’s opening mechanism.

An airbag for seat belts: the beltbag

The beltbag is an inflatable seat-belt strap that is able to reduce the risk of injury to passengers in the rear in a head-on collision by lessening the strain placed on the ribcage.

Should the crash sensors detect a severe frontal impact, the airbag control unit will trigger deployment and inflation of the beltbag. A gas generator then inflates the multi-layered belt strap with Velcro seams to nearly three times its normal width. The resulting larger surface area is able to better distribute the force acting on the seat occupant, thereby reducing the risk of injury.

The beltbag is used in exactly the same way as a conventional seat belt. The belt strap’s design is different from that of the standard belt though, and received praise in practical trials for being extremely comfortable to wear and for its extra-soft belt strap edge.

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